What is myelofibrosis (MF)?

Myelofibrosis (MF) is a type of blood cancer that affects the bone marrow. Bone marrow is where blood cells are made. In MF, scar tissue builds up inside the bone marrow. This stops the bone marrow from working properly.

Most people with MF have low levels of blood cells. But some people with MF have low levels of some types of blood cells and high levels of other types.

When there are fewer blood cells being made in the bone marrow, other organs in the body start to make them. This is usually the spleen and liver. These organs get bigger as they make blood cells.

MF can happen at any age, but it is more common in people over the age of 60.

To understand MF and its treatment, it can help to know more about the blood and bone marrow.

Related pages

Types of myelofibrosis

  • Primary myelofibrosis (pMF)

    MF can happen in people who have never had problems with their bone marrow before. This is called primary myelofibrosis (pMF).

  • Post-ET myelofibrosis 

    MF can develop in people who have essential thrombocythaemia (ET). This is called post-ET myelofibrosis.

  • Post-PV myelofibrosis 

    MF can also develop in people who have polycythaemia vera (PV). This is called post-PV myelofibrosis.

Related pages

Symptoms of myelofibrosis (MF)

Some people are diagnosed with MF when they have a blood test for another reason. But most people are diagnosed after going to see their GP with 1 or more symptoms. These may include:

  • feeling very tired (fatigue)
  • feeling breathless
  • high temperature (fevers) and drenching night sweats requiring a change of clothes or bed covers
  • unexplained weight loss
  • itchy skin (often after a warm bath or shower)
  • achy or tender bones and joints
  • discomfort in the tummy area (abdomen)
  • feeling full soon after beginning to eat
  • abnormal bleeding or bruising
  • getting infections.

Possible complications of MF

Some people also develop symptoms because of the complications of MF.


When the body tries to break down (get rid of) more blood cells than usual, it can cause a painful condition called gout. Gout affects the joints. It causes pain, heat, redness and swelling. It usually only affects the big toe joint. But it can affect other joints, especially in the hands and feet.

Gout is caused by uric acid building up in the blood. Uric acid is produced when lots of cells are broken down. The uric acid forms crystals that get into the joint and cause the symptoms.

Usually, the kidneys can clear uric acid from the blood and pass it out of the body in the pee (urine). But sometimes, they cannot cope with large amounts.

Your doctor can check the level of uric acid with a blood test. Depending on the result, they may give you a tablet called allopurinol to help prevent gout.

Enlarged spleen

The spleen sits on the left side of the tummy (abdomen), just under the ribs. It is usually about the size of a fist.

The spleen
Image: The spleen

The spleen:

  • helps fight infection
  • stores and breaks down blood cells.

MF can cause the spleen to grow bigger than normal. This is called an enlarged spleen. Sometimes, this causes symptoms. These include discomfort on the left side of the tummy and feeling full quickly when eating.

Having an enlarged spleen can cause problems. It may:

  • keep blood cells in the spleen instead of releasing them into the blood
  • destroy blood cells.

Both these changes can reduce the number of blood cells in the blood.

Blood clots

Some people with MF have a higher risk of developing a blood clot. Symptoms of a blood clot include:

  • throbbing pain, redness or swelling in a leg or an arm
  • suddenly feeling breathless or coughing
  • sharp chest pain, which may be worse when you cough or take a deep breath.

If you have any of these symptoms, contact the hospital straight away. If you cannot speak to your doctor, call the NHS urgent advice number on 111.

A blood clot is serious, but it can be treated with drugs that thin the blood (anti-coagulants). Your doctor or nurse can give you more information. You may be given drugs to help prevent a clot.

Blood clots can also cause heart attacks and strokes. If you think you may be having a heart attack or stroke, call 999 for an ambulance or go straight to A&E (emergency department).

Bleeding or bruising

Sometimes, MF can cause abnormal bleeding or bruising. Any bleeding might be heavier than normal and take longer to stop.

Symptoms may include:

  • nosebleeds
  • bleeding gums
  • heavy periods
  • blood in your pee or stools (poo)
  • very dark poo
  • blood in your vomit (sick) – this can be a bright red liquid or look like brown or black coffee granules
  • tiny red or purple spots on your skin that may look like a rash.

Tell your doctor if you notice any signs of abnormal bleeding or bruising.

If you think you see blood in your sick or poo, or if you have dark poo, or if any bleeding is heavy or will not stop, contact a doctor urgently. If you cannot speak to a doctor, call 999 for an ambulance or go straight to A&E.

Acute myeloid leukaemia (AML)

Some people with MF develop acute myeloid leukaemia (AML). AML is a blood cancer, which can get worse quickly if it is not treated. It can cause similar symptoms to MF. But the symptoms of acute leukaemia develop more quickly and can be more severe.

Not everyone with MF has the same risk of developing AML. Your doctor can tell you more about this.

Diagnosis of myelofibrosis (MF)

If your doctor thinks you may have MF, they will refer you to the hospital to see a specialist blood doctor called a haematologist. At your hospital appointment, you may also meet a clinical nurse specialist. They may be your key worker. This means they are your main contact for information and support.

Depending on your symptoms and blood tests, your haematologist may be able to diagnose MF straight away. Or they may need to do tests to rule out other conditions.

Your haematologist will decide whether you need further tests. This can include more blood tests and a bone marrow biopsy

  • Full blood count (FBC)

    This blood test counts the numbers of red blood cells, white blood cells and platelets in your blood.

    About 10 in a 100 people (10%) with primary myelofibrosis do not have a change in any of these genes. This is called triple negative MF.

  • Bone marrow biopsy

    Your doctor may want to take a sample of bone marrow to look at under a microscope. This is called a bone marrow biopsy. Doctors usually remove the sample from the back of the hip bone (pelvis).

    The sample is sent to the laboratory to be checked for abnormal cells.

  • Genetic tests

    Genes carry the instructions that cells in the body need to work properly. There are genes that control how many blood cells are made in the bone marrow. Genes can develop changes over time. Genetic changes do not always cause problems, but they can cause conditions such as MF.

    You may have blood tests to look for changes in the following genes

    • JAK2 – around 60 out of 100 people with primary MF (60%) will have this change
    • CALR – around 25 out of 100 people with primary MF (25%) will have this change
    • MPL – around 8 out of 100 people with primary MF (8%) will have this change.

    Some people with MF do not have any of these genetic changes. This is called triple negative MF.

  • Scans

    You may have a scan to show whether your spleen or liver is enlarged. You may also have a scan if blood is being made anywhere outside your bone marrow.

    You may have 1 or more of the following scans:

    • An ultrasound scan uses sound waves to build up a picture of the organs inside the tummy and pelvis. You may have an ultrasound to check for an enlarged spleen.
    • A CT scan takes a series of x-rays that build up a 3D picture of the inside of the body
    • An MRI scan uses magnetism to build up a detailed picture of areas of the body. 

Your doctor or nurse will tell you more about these tests.

Waiting for test results can be a difficult time. It may help to talk to your family, friends or specialist nurse.

Risk groups for myelofibrosis (MF)

MF is divided into different risk groups. These can describe:

  • how quickly or slowly MF may develop
  • the risk of it developing into leukaemia.

Your MF risk group is based on several things, including:

  • your age
  • your symptoms
  • whether you have anaemia (low levels of red blood cells)
  • the number of white blood cells in your blood
  • the number of immature (blast) cells in your blood
  • the results of genetic tests.

MF can be graded as low, medium (intermediate) or high risk. Knowing your risk group can help you and your doctor choose the best treatment options for you.

Treatment for myelofibrosis (MF)

Before treatment, a team of health professionals work together to plan the treatment they feel is best for you. This team is called a multi-disciplinary team (MDT). The MDT look at your test results, your risk group and general health.

Your doctor will talk with you about your treatment options and the possible risks and benefits before you agree (consent) to have treatment.

MF cannot usually be cured. In some people, it can stay the same for many years without causing problems. In others, it can become more serious or even life threatening.

Treatment for MF is usually given to help with symptoms or prevent complications. It can also be given to control or slow down the condition. You may be offered treatment as part of a clinical trial.

If you do not have symptoms or your risk group is low, you may not need treatment for a while. But your haematologist will monitor your condition regularly. If you develop any symptoms between appointments, tell your haematologist or clinical nurse specialist.

Treatment to control myelofibrosis (MF)

Treatment can be given to control MF, including targeted therapy, immunotherapy, chemotherapy and a donor stem cell transplant (allogeneic transplant).

Targeted therapy and immunotherapy for MF

Targeted therapies are drugs that block the growth of cancer cells. They do this by affecting how cancer cells grow and divide.

Immunotherapy drugs use the immune system to find and attack cancer cells.

Different types of targeted therapy and immunotherapy are used to treat MF.

  • JAK inhibitors

    Ruxolitinib (Jakavi®) and fedratinib (Inrebic®) are targeted therapy drugs called JAK inhibitors. They target the genes that help the abnormal blood cells in MF grow. Both are taken as tablets.

    You may be given a JAK inhibitor to help with symptoms. If you have intermediate-risk or high-risk MF, it can also reduce an enlarged spleen.

    Side effects of JAK inhibitors include anaemia and fewer platelets in the blood. It can also reduce the white blood cells in your blood. This can make you more likely to get an infection. If this happens, the treatment may need to be reduced or stopped for a while.

    You will be given a 24-hour telephone number for the hospital. You should use this number if you have any symptoms or side effects. Your haematologist and clinical nurse specialist can talk to you about this. It is important you follow any specific advice your cancer team give you.

  • Thalidomide

    Thalidomide works in several different ways to target abnormal blood cells. It acts as a type of targeted therapy and a type of immunotherapy. Thalidomide comes as capsules. You may have it on its own or with steroid tablets. Thalidomide can cause problems for an unborn baby. Your haematologist, clinical nurse specialist or pharmacist will talk to you about making sure you do not get pregnant or make someone pregnant while taking thalidomide.

  • Interferon alpha

    Interferon is a protein that is made naturally by the body. It can also be made as a drug (interferon alpha) and given as an injection under the skin (subcutaneously). It slows down how quickly the bone marrow makes blood cells..

Chemotherapy for MF

Chemotherapy  uses anti-cancer (cytotoxic) drugs to destroy cancer cells. It can help reduce the size of the spleen and the liver. It also helps control other symptoms and may increase the number of blood cells. But chemotherapy is not suitable for everyone with MF because it can cause low blood cell counts.

If you have chemotherapy, your doctor monitors you closely and you have blood tests to check your blood cell counts. Sometimes, treatment needs to be stopped if blood cell counts become too low.

Hydroxycarbamide (HC) is a chemotherapy drug often used to treat MF.

Taking HC for a long time can increase the risk of getting skin cancer. It is important that you protect your skin from the sun. You should also check for any changes in your skin during and after treatment with HC. Your haematologist or clinical nurse specialist can tell you more about this.

Another chemotherapy drug called busulfan may sometimes be used. You take it as a tablet. The side effects are like the side effects of HC. Taking busulfan for a long time may slightly increase the risk of developing leukaemia.

Your haematologist and clinical nurse specialist can talk to you about the side effects of chemotherapy.

Donor stem cell transplant (allogeneic transplant)

A small number of people with higher-risk MF may be able to have a donor stem cell transplant. This treatment replaces bone marrow that is no longer working properly with healthy stem cells from another person (donor). These new stem cells make healthy red and white blood cells and platelets.

This treatment can sometimes cure MF. But it can also cause serious side effects, so it is not suitable for most people. Your general health needs to be good. Your haematologist will talk to you about the risks and benefits of donor stem cell treatment if this is a possibility for you.

Supportive treatments

Supportive treatments can be used to help with the symptoms or complications of MF.

Treatment for anaemia

You may feel weak, tired or breathless. This is caused by low levels of red blood cells (anaemia). You can have blood transfusions or drugs to help.

  • Blood transfusions

    You may have blood transfusions to increase the number of red blood cells in your blood. You can usually have a blood transfusion as a day patient. Most people can have blood transfusions as often as they are needed.

  • Drugs to treat anaemia
    • Erythropoietin (EPO) is a drug called a growth factor. Growth factors are made naturally by the body. But they can be made as a drug to stimulate the bone marrow to make more blood cells. Erythropoietin may help increase the level of red blood cells in your blood and reduce the number of blood transfusions you need. You have it as an injection under the skin. A nurse can sometimes teach you how to give it yourself.
    • You may be given tablets called danazol to help improve anaemia. Danazol is a hormone made by the body to stimulate it to produce red blood cells. Danazol can also be made as a drug. It is not as commonly used as EPO.
    • Steroids are drugs sometimes used to treat low levels of red blood cells.

Aspirin to prevent blood clots

Most people with MF are treated with aspirin tablets. Aspirin affects the way platelets stick together and helps prevent blood clots. Drugs that prevent clots are called anti-platelet drugs or blood thinners. Aspirin does not affect the number of platelets in the blood.

One of the side effects of aspirin is an increased risk of bleeding and ulcers in the stomach.

If you are taking aspirin, ask your doctor for advice about painkillers. Certain types of painkillers, such as ibuprofen, may not be suitable for you while you are taking aspirin.

If you cannot take aspirin because of medical conditions such as a stomach ulcer, you may be given another anti-platelet drug instead.

Other treatments for an enlarged spleen

Chemotherapy is the most common treatment if you have symptoms caused by an enlarged spleen. But other treatments are sometimes used.

  • Radiotherapy

    Radiotherapy uses high-energy rays to destroy cancer cells. It can help improve symptoms, such as pain and a high platelet count. But the effects may only last for a few months.

    Radiotherapy can cause temporary side effects, but they are usually mild. They include tiredness and skin irritation.

  • Removing the spleen (splenectomy)

    If your spleen is enlarged and causing symptoms, your specialist may talk to you about having surgery to remove it.

    There can be advantages and disadvantages to having this operation. Your specialist will talk to you about this before you decide.

Pregnancy fertility and myelofibrosis (MF)

If you are planning to get pregnant or to make someone pregnant in the next few months, talk to your doctor first.

Chemotherapy and some other treatments may affect the development of an unborn baby. Doctors usually advise against getting pregnant or making someone pregnant during these treatments and for a few months after. It is important to use effective contraception.

Chemotherapy may affect fertility. If this is a concern for you, talk to your doctor before starting treatment.

If you are planning to get pregnant, MF can increase the risks of complications during pregnancy. But with risk-reducing treatments and careful monitoring during pregnancy, most babies are born healthy. Your haematologist and obstetrician (doctor who specialises in pregnancy) will work together to give you the best care during your pregnancy.

During pregnancy, your doctor usually advises you to take aspirin daily. This reduces the risk of complications from blood clots for both you and the baby. If you need other treatment to reduce your risk of complications, your doctor may advise having interferon alpha.

Living with myelofibrosis (MF)

If you have MF, you need regular check-ups and blood tests. If you are worried or notice new symptoms between appointments, tell your haematologist or clinical nurse specialist as soon as possible.

Your feelings

Everyone has their own way of dealing with the different feelings they experience. You may find it helpful to talk about things with family members, friends, or your specialist doctor or nurse.

Macmillan is also here to support you. If you would like to talk, you can:

The organisations below also offer information and support: 

  • MPN Voice

    MPN Voice is a support network for people with myeloproliferative neoplasms (MPNs). It provides information and support.

  • Leukaemia Care

    Leukaemia Care is a national blood cancer support charity for people with leukaemia and other blood disorders. It has regional support groups.

  • Blood Cancer UK 

    Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

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We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 March 2023
Next review: 01 March 2026
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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